Tumor-intrinsic mechanisms that have been identified to impair γδ T cell attack include the release of large amounts of prostaglandin E2 by tumor cells with strong expression of cyclooxygenase-2 (COX-2),151 the activity of indoleamine-2,3-dioxygenase (IDO) and its metabolite kynurenine,225 the release of galectin-3,226 and the hypoxic tumor microenvironment.227 Inhibitors for the respective pathways can enhance tumor killing by Vδ2T cells in vitro, and it seems reasonable to propose that these strategies can also work in vivo, given the availability of approved drugs such as COX2 inhibitors. This evidence concerns the gene IDO1 and neoplasm.